Callisto, which is about the size of the planet Mercury, is one of Jupiter's four giant moons, which include Europa, Io and Ganymede. Jupiter has a dozen smaller moons and maybe dozens more smaller satellites with irregular outlying orbits.

Callisto's icy surface is the most heavily cratered of any moon in the solar system. It is geologically dead with no evidence of volcanoes, tectonic plates or ice lakes, unlike its sister moons. Of Jupiter's four largest moons, Callisto orbits farthest from the giant planet.

The picture was taken in May 2001 by the Galileo spacecraft, which has been orbiting Jupiter since December 1995.